If only The Druggist of Auschwitz were fiction. The book’s sole imaginary character, however, is the narrator, Adam Salmen. Said to be the “last Jew of Schässburg,” (now Sigişoara, Romania), Adam’s occasional commentary coils through ghastly fact.

The core of the book is Dieter Schlesak’s arrangement of witness testimony and historical research about the 1963-1965 Frankfurt Auschwitz trial, with Victor Capesius as one of the defendants. Capesius, the chief pharmacist at Auschwitz, is the “druggist” of the title. Through Capesius and his comrades, Schlesak documents the Nazis’ grotesque perversion of the Hippocratic Oath.

In our world, the words “pharmacist” and “druggist” connote therapy and healing. But in the hell that was Auschwitz, it was doctors and other health professionals, led by Joseph Mengele, who ensured the efficiency of the death machine. Nazi medical professionals stood on the ramp as the cattle cars rolled in bearing over a million Jews and 20,000 Gypsies from across Europe. They made the selections on who would live and who would die. Nazi dentists pulled the teeth with gold crowns out of the mouths of people on their way into the gas chamber. Nazi “medics” poured the canisters of Zyklon B into the sealed chambers of death. Nazi doctors injected chloroform into the hearts of adults and children, especially twins, to kill them for onsite medical experimentation.

As Schlesak painstakingly catalogues, any number of characteristics were immediate qualifications for “selection” to the gas chamber – scars and bodily imperfections, old age, youth, infancy, pregnancy, being female, sickness, broken limbs, and most important – the whim of the selector on duty. Within the small minority of prisoners allowed to live, Jewish medical professionals had a slight edge. If they had the foresight to speak up as they arrived, they might be chosen for jobs such as cleaning the gold from victims’ teeth. Or, in the case of Miklós Nyiszli, briefly profiled toward the end of the book, performing dissections on Dr. Mengele’s newly murdered patients.

The Druggist of Auschwitz is interspersed with photographs of witnesses, Capesius, and the death camp itself. The inclusion of photographs resonates with the work of another German writer straddling the line between fact and fiction – W. G. Sebald, whose Austerlitz reads like a memoir in which the author purports to unearth his long repressed experiences flowing from the British kinder transport. In contrast to Schlesak, however, Sebald creates a parallel world that is credible because of its attention to historical and psychological detail.

The Druggist of Auschwitz recounts unadorned truth. Here the devil is, in fact, in the details. In the strict punctuality of the elevator operators removing the newly gassed bodies (they were not always dead) for incineration, to make room for the next transport. In the daughter, designated to live, who joins her mother in the gas chamber so that her mother will not die alone. In the Red Cross trucks, carrying canisters of Zyklon B to the gas chamber. In the organized killings of hundreds against the “Black Wall,” where it was determined that the shooters would be less upset if the guns had silencers on them.

In portraying the leisure activities of the SS officers at Auschwitz, Schlesak quotes Roland Albert, his distant relative. “As a sideline I was a religion teacher, when my guard duty allowed. My wife taught music in the main school. … It was life like anywhere else. We planted a vegetable garden, kept bees, planted flowers, went hunting and fishing, there were afternoon coffee parties, birthdays, Christmas parties with Commandant H[ess].”

In detailing the meticulous record keeping, Schlesak shows the log listing each train and its number of victims, with Capesius’ annotations in the margins. He enumerates the cost of a canister of Zyklon B. Witnesses speak to the sorting of the possessions of all who entered the gates, whether or not they were gassed – clothing and shoes in one place, currency in another, gold and jewels somewhere else. A centerpiece of Capesius’ trial was the question of his significant postwar wealth. Capesius vigorously denied that his riches came from Auschwitz victims.

What is new here? Schlesak is certainly not the first to document this destruction of humanity. As Primo Levi wrote in Survival in Auschwitz, “Then for the first time we became aware that our language lacks words to express this offence, the demolition of a man. … Nothing belongs to us anymore; they have taken away our clothes, our shoes, even our hair; if we speak, they will not listen to us, and if they listen, they will not understand.” Nor is Schlesak the first to chronicle the complete disconnection between the perpetrators’ actions and their later disavowal of personal responsibility. There can be no colder account of this phenomenon than Hannah Arendt’s Eichmann in Jerusalem. What is new in The Druggist of Auschwitz is the use of Victor Capesius – an unknown figure to most readers – to remind us once again of man’s infinite capacity for evil. Schlesak does a masterful job of intermingling eyewitness testimony of Capesius’ role in the selection and killing process with Capesius’ revisionist account, partly obtained from interviews that Schlesak conducted himself.

Another innovation is the organization of the book itself. It seems beside the point to consider the literary merits of such horrifying material, but the title begs the question – Is this a novel? Schlesak constructs the book in nine parts, with some chapter headings reading like a history text: “The Auschwitz Dispensary,” “The German Obsession with Racial ‘Purity’ and the German Language as a Cure.” Carefully ordered historical material ensures that no group is spared from harsh examination. A German populace trained to obey authority enabled the scale and efficiency of the killing. But there are other human realities as well. What did it take to survive? Adam, the fictional narrator, is a “Sonderkommando” (German for “Special Unit”) – prisoners considered able bodied at selection who were given the job of removing bodies from the crematorium. These Jewish prisoners were intimately involved with the killing, although not themselves the killers. Adam’s terse remarks buttress the testimony of real life Sonderkommandos who speak about the relentlessness of the killing, and their role in the “clean up.” Using factual data, Schlesak exposes the role of Jewish councils in guaranteeing that the lists of Jews in their respective communities were accurate before turning over this information to the Nazis, enabling Jews to be rounded up with ease. On the flip side, he considers the madness of Hitler’s relatives as a factor in Hitler’s insane drive to disavow his past: he was not German (he was Austrian); he was not Aryan (he likely had Jewish ancestry); he was not light skinned or blond.

If a historian’s role is to document the past’s realities so that future generations can see the truth, then this is a historical work. If a fiction writer’s role is to expose the truths that motivate human activity, then this is a work of fiction. In the end, does the distinction matter? Schlesak has succeeded in organizing this confronting material in a way that compels us to read it. The power is in making the unbelievable believable.

It is difficult to understand how life goes on after Auschwitz. And yet it does. There are authors like Viktor Frankl and the recently deceased Arnošt Lustig who found a calling in identifying and recording the humanity within the horror. And then there are others, like Simon Wiesenthal, who made it a profession to hunt Nazis, but still took the time to explore the possibilities and limits of forgiveness in The Sunflower.

We cannot and should not forget. The Druggist of Auschwitz makes an important contribution toward that end, with John Hargrave’s translation communicating this raw material in a way that once again forces us to examine how ordinary people can descend to such terrifying depths.

Martha Toll is Executive Director of the Butler Family Fund, a nationwide philanthropy focused on ending homelessness and the death penalty. She writes novels and has been featured as a book commentator on NPR.